In the recovery of oil from oil-containing formations, it usually is possible to recover only minor portions of the original oil in-place by the so-called primary recovery methods which utilize only the natural forces present in the formation. Thus, a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean formations. These techniques include thermal recovery methods, waterflooding, and miscible flooding.
More recently, carbon dioxide has been used successfully as an oil recovery agent. Carbon dioxide is a particularly desirable material because it is highly soluble in oil, and dissolution of carbon dioxide in oil causes a reduction in the viscosity of the oil and an increase in the volume of oil, all of which improve the recovery efficiency of the process. Carbon dioxide is sometimes employed under non-miscible conditions. In certain reservoirs it is possible to achieve a condition of miscibility at reservoir temperature and pressure between carbon dioxide and the reservoir oil.
Where carbon dioxide is used in a formation having swept and unswept zones, the swept zone will create a situation where carbon dioxide does not contact oil contained in the unswept zone. The carbon dioxide thus has a tendency to overrride or bypass the unswept zone leaving behind oil contained in the unswept zone. Moreover, low pH conditions encountered in a carbon dioxide flood affect the long term stability of many agents used to divert carbon dioxide through an unswept zone.
To overcome this situation, a method is needed which will close pores in a substantially low pH swept zone which has been contacted with carbon dioxide and thereafter divert carbon dioxide to the unswept zone which has not been contacted so as to remove hydrocarbonaceous fluids therefrom.